Arc Distribution During the Vacuum Arc Remelting of Ti-6Al-4V
- PDF / 973,517 Bytes
- 12 Pages / 593.972 x 792 pts Page_size
- 64 Downloads / 226 Views
E vacuum arc remelting process is extensively utilized in the commercial production of Ti-6Al-4V ingots. Overall, the goal of the process is to increase the homogeneity and purity within the formed ingot. In the first stage of melting, compacted and welded titanium sponge containing the appropriate alloying elements is melted in a VAR furnace in what is commonly referred to as the primary melt. This material is subsequently remelted within a VAR furnace, and if this is the final melt, then it is referred to as a double VAR melt. Some applications, such as rotating parts in jet aircraft engines, require an additional VAR melt, and this is referred to as a triple VAR melt. An intermediate melt stage using an electron-beam (EB) furnace is also sometimes employed. One advantage of the vacuum arc remelting process over vacuum induction melting, for instance, is better melting rate control. This leads to a more tightly controlled solidification and an overall axially orientated solidification front. Figure 1 shows a cross section of a typical coaxial VAR furnace. The input material, commonly referred to as the electrode, is melted by means of a metal vapor plasma arc that strikes from the electrode to the forming ingot. The furnace is referred to as coaxial when the power supply return feed is attached around the circumference of the crucible flange. Ideally, C. RIGEL WOODSIDE, General Engineer, and PAUL E. KING, Business and Outreach Manager, are with the National Energy Technology Laboratory, Albany, OR 97321-2152. Contact e-mail: [email protected] CHRIS NORDLUND, Quality Assurance and Technology Manager, is with ATI Albany Operations, Albany, OR 97322-3828. Manuscript submitted January 12, 2011. Article published online December 7, 2012. 154—VOLUME 44B, FEBRUARY 2013
the effect of this arrangement is that a centered arc will produce no net magnetic field external to the crucible because the current in the crucible is pointed in the opposite axial direction to the current in the electrode. The electrode is the cathode and the ingot is the anode. The primary mechanism for heating via arcs is simply concentrated joule heating, and the potential drop across the electrode gap is typically in the 30 V to 50 V range during industrial production. It is important to realize that the arcs do not extensively vaporize the material; rather, the heated material drips off the end of the electrode and into the ingot as a bulk transfer process. For this reason, it is recognized that the VAR process is not as effective at removing some of the heavier type 1 inclusions from the material as compared to EB melting.[1] The geometry of a VAR furnace is such that there is no direct view of the electrode arc gap region. For titanium alloy melting, gap lengths are on the order of a few centimeters. The positions and in turn distribution of arcs is not directly controlled, and arcs are free to move about. The video cameras looking down the annulus of the furnace give some indication of the arc dynamics. This is monitored by an operator but is t
Data Loading...
